Examine the command output, debug logs, and system logs for a more detailed message on the error.

See "Setting Media Manager debug logging to a higher level" in the NetBackup Logging Reference Guide.

Investigate the system log messages that are related to the error leading to the media mount failure.

Verify that all of the Media Manager binaries are at a compatible version level. Verify that robotic interfaces to the vendor and operating system hardware and software have compatible versions.